1. Field of the Invention
The present invention relates to a gas generator for an air bag, in which, when gas generating agents are burnt in two stages, a rising rate of a pressure becomes moderate, a change in pressure is small and an impact to a vehicle occupant can be small. The present invention is also directed to an air bag system that incorporates the gas generator.
2. Description of the Related Art
An air bag system mounted on various kinds of vehicles and the like such as automobiles, aims to hold an occupant by an air bag (a bag body) rapidly inflated by a gas when the vehicle collides at a high speed and to prevent the occupant from crashing into a hard portion inside the vehicle such as a steering wheel, and a windscreen due to an inertia, and getting injured. This kind of air bag system generally comprises a gas generator actuated upon a collision of the vehicle to discharge a gas, and an air bag to which the gas is introduced to inflate.
It is desirable that such an air bag system can safely restrain the occupant even when the frame of the occupant (for example, whether a sitting height is long or short, whether an adult or a child, and the like), a sitting posture (for example, a posture of holding tightly on the steering wheel) and the like are different. For this reason, a so-called dual inflator, which inflates an air bag in two stages by generating a gas in two stages, has been employed.
Gas generators applied to such an air bag system are disclosed in JP-A 08-207696, U.S. Pat. No. 4,998,751, U.S. Pat. No. 4,950,458, and the like. JP-A 08-207696 discloses a gas generator in which two kinds of gas generating agent capsules are ignited by one igniter to generate a gas in two stages. U.S. Pat. No. 4,998,751 and U.S. Pat. No. 4,950,458 disclose gas generators in which two combustion chambers are provided to control actuation of the gas generator, and a gas is generated in two stages due to an expanded flame of a gas generating agent.